My Victron MultiPlus-II ESS suddenly charged the battery from the grid at 3 kW on a Sunday morning, with the SOC at 28 %. Why, and can I stop it or slow it down?

Plain explanation

Victron's ESS manual lists several reasons ESS charges the battery from the grid by itself. First, it recharges when the SOC drops 5 % or more below the 'Minimum SOC' set in the ESS menu, and stops once it is back at the minimum. Second, with BatteryLife on, a run of poor solar days makes the system raise the low SOC limit by 5 % per day, so a 28 % SOC can suddenly be 'too low'. Third, if the battery voltage falls below the sustain level, ESS charges from the grid at up to 5 A per unit. Scheduled charge levels and a charge request from the battery's own BMS (for example for balancing) can also start a grid charge. The GX overview shows a status reason code (for example #2 BatteryLife active) that tells you which one it was. To avoid surprises, set the minimum SOC on purpose, check whether BatteryLife is on, and review any scheduled charges in the ESS menu.

Steps from the source

1. Open the Cerbo GX overview and note the ESS reason code (#1 SOC low, #2 BatteryLife active, #5 slow charge …)
2. Check Settings › ESS: Minimum SOC and whether BatteryLife is on; check the current dynamic SOC limit
3. Check scheduled charge levels in the ESS menu
4. Check the battery BMS log for a balancing or calibration charge request
5. Review VRM history around the event to match SOC, voltage and the reason code

"The system will automatically recharge the battery (from the grid) when the SOC drops 5% or more below the value of ‘Minimum SOC’ in the ESS menu. Recharge stops when it the battery is recharged up to the Minimum SOC level."

Word for word from the source.

Source

Where installers ask this

• VICTRON MultiPlus-II 48/5000/70-50 … lädt auf einmal aus dem Netz obwohl SOC bei 28 % war (photovoltaikforum.com)

General guidance based on the manufacturer's manual or the named source. Always follow the current manual for your exact model and your national code. DC and AC electrical work is for qualified installers only. Not affiliated with or endorsed by any brand named; trademarks belong to their owners.